Received: 18 April 2019
Accepted: 30 October 2019
First Online: 8 November 2019
Ethics approval and consent to participate
: The study was approved by the institution review board in Gangnam Severance Hospital, which waived the requirement for informed consent because of retrospective data collection without personally identifiable information (IRB approval No: 3–2018-0139).
: Not applicable.
: The authors declare that they have no competing interests.